In recent years, many kinds of herbicidal agents have been provided and used in practice and have made great contributions in reducing the labor power or works in the agriculture and in improving the yields of the agricultural products.
Still, most of the known herbicidal agents are not completely satisfactory but can show some problems in respect of their herbicidal effects and their safety to man and phyto-toxicity to crop plants upon the actual application to the agricultural fields. For instance, perennial weeds such as purple nutsedge (Cyperus rotundus) and Johnson grass (Sorghum halepense) grow widely in the agricultural fields over the world, and it is known that these perennial weeds are difficult to be controlled or killed. Accordingly, many kinds of herbicidal agents have been provided and applied to combat or control the growth of perennial weeds. However, these known herbicidal agents or compounds which have been employed for control of the perennial weeds are not yet entirely satisfactory, since their herbicidal effects are not necessarily sound and their phyto-toxicity to the crop plants are sometimes objectionable. In these circumstances, the demand for new herbicidal agents having more improved properties is lasting. In particular, as herbicidal compounds containing a pyrimidine nucleus is known 2-(3'-bromo-phenoxy)-5-chloropyrimidine (see Japanese patent application (unexamined) first publication "Kokai" No. 55729/79 corresponding to U.S. Pat. No. 4,427,437). This particular herbicidal compound can show such drawback that its herbicidal activity is low against the above-mentioned perennial weeds, including purple nutsedge and Johnson grass.
In an attempt to provide such new herbicidal compounds which are effective to combat or kill not only the annual weeds but also the perennial weeds, we, the present inventors, have made our extensive researches on 2-phenoxypyrimidine derivatives. As a result, we have succeeded in synthetizing a class of new 2-phenoxypyrimidines having some substituents introduced at the specific positions of the pyrimidine ring and the benzene ring thereof, which are represented by the general formula (I) given hereinafter. We have now found that the new 2-phenoxy-pyrimidine derivatives of the general formula (I) now synthetized are able to exhibit high herbicidal activities not only to a wide variety of annual weeds but also to a variety of perennial weeds, including purple nutsedge and Johnson grass, and also that the new compounds of the formula (I) are of no or little phyto-toxicity to many kinds of crop plants and can be applied to the agricultural fields with very much high safety, so that the new compounds of the formula (I) are useful as a herbicidal agent having the unexpectably excellent properties.